Design and implementation of auto-tracking system for FSO link under pointing error

The performance of free space optical (FSO) communication is primarily dependent on atmospheric turbulence and pointing errors, where pointing error compromises of boresight error and jitter. However, most of the existing work considered pointing error by counting zero-boresight error or jitter while evaluating the performance of FSO communications. In this paper, a generalized distribution, Nakagami-m fading, for the radial displacement of pointing error is considered by taking account of both boresight and jitter error for performance analysis of FSO communication. Two subsequent auto-tracking mechanisms are designed and developed at the transmitter to combat the issues of boresight error and jitter. First is a coarse tracking system to minimize the boresight error and second is fine tracking to remove leftover boresight error known as jitter. FSO received power is continuously monitored, and the link status is feedback to the transmitter via the RF link to initiate the corresponding tracking. The proposed auto-tracking mechanism has experimented with a wide range of non-zero boresight angles, which is from ± 10\(^{\circ }\) to ± 180\(^{\circ }\) with a fine-tuning of horizontal displacement up to ± 8 cm from the receiver center. A closed-form outage probability is derived over generalized phenomenon where the analytical results are compared with simulation, measurement, and with existing methods.